In recent years, various flat panel display devices with a smaller weight and a smaller size when compared with cathode ray transistors have been developed.
In various flat panel display devices, since active matrix organic light-emitting diode (AMOLED) display devices use a self-illuminating organic light-emitting diode (OLED) to display an image, they typically have properties such as short response time, low power consumption for driving, and a relatively better brightness and color purity. In view of this, organic light-emitting devices have become the focus of the display technology of the next generation.
With regard to a large AMOLED display device, a plurality of pixels located in a cross region of a scan line and a data line is included. Each pixel includes an OELD and a pixel circuit used for driving the OELD. The pixel circuit typically includes switch transistors, driving transistors and storage capacitors.
Since the pixel properties of AMOLEDs are influenced by the difference between driving transistors and the leakage current of the switch transistors, an image displayed by such a plurality of pixels has a relatively poor quality uniformity and consistency.
FIG. 1 is a schematic view of a pixel of an active matrix organic light-emitting diode (AMOLED) display device in the prior art. As shown in FIG. 1, the transistor of the pixel circuit 112 thereof is a PMOS transistor (a MOS transistor which has an n-type substrate and a p-channel and transfers current through hole migration).
The pixel 110 of the AMOLED display device includes: an OLED, and a pixel circuit 112 connected to a data line Dm and a scanning control line Sn1 to control the OLED.
An anode of the OLED is connected to the pixel circuit 112, and a cathode of the OLED is connected to a second power supply ELVSS. The OLED emits light with a corresponding brightness to the current intensity provided by the pixel circuit 112.
When providing a scanning control signal to the scanning control line Sn1, the pixel circuit 112 controls the amount of current provided to the OLED correspondingly to the data signal provided to a data line Dm. To this end, the pixel circuit 112 includes a second transistor T2 (i.e., a driving transistor) connected between a first power supply ELVDD and an anode of the OLED (Organic Light-Emitting Diode), a first transistor T1 (i.e., a switch transistor) connected between a gate of the second transistor T2 and the data line Dm, and a first capacitor C1 connected between the gate of the second transistor T2 and the first power supply ELVDD, wherein the gate of the first transistor T1 is connected to the scanning control line Sn1.
The gate of the first transistor T1 is connected to the scanning control line Sn1, and the source (or the drain) of the first transistor T1 is connected to the data line Dm. The drain (or the source) of the first transistor T1 is connected to one terminal of the first capacitor C1 (the other terminal thereof is connected to the first power supply ELVDD). When a scanning control signal is provided from the scanning control signal line Sn1 to the first transistor T1, the first transistor T1 is turned on, and a data signal provided from the data line Dm is provided to the first capacitor C1. At this time, a voltage corresponding to the data signal is stored in the first capacitor C1.
The gate of the second transistor T2 is connected to one terminal of the first capacitor C1 (the other terminal thereof is connected to the first power supply ELVDD), and the source of the second transistor T2 is connected to the first power supply ELVDD. The drain of the second transistor T2 is connected to the anode of the OLED. The second transistor T2 controls a current flowing to the second power supply ELVSS from the first power supply ELVDD via the OLED, and the current intensity corresponds to the voltage stored in the first capacitor C1.
One terminal of the first capacitor C1 is connected to the gate of the second transistor T2, and the other terminal of the first capacitor C1 is connected to the first power supply ELVDD, and a voltage corresponding to the data signal is charged into the first capacitor C1.
The pixel 110 controls the brightness of the OLED by adjusting the current supplied to the OLED correspondingly to the voltage discharged into the first capacitor C1, and an image with a predetermined brightness is displayed. However, in such a traditional AMOLED display device, due to the change in threshold voltage of the second transistor T2 and the leakage current of the first transistor T1, it is difficult to display an image with a uniform brightness. For example, in different pixels, due to the difference in threshold voltage of the second transistor T2 and the difference in first power supply ELVDD, the current flowing through the OLED is inconsistent when a same gate driving voltage is applied, leading to inconsistency in the brightness of the OLED. Each pixel generates light of different brightness in response to a same data signal, and as a result, the displayed image hardly has a uniform brightness.